On 06/02/2020 14:00, Commander Kinsey wrote:
Why do barometers have different centre readings? I thought 1000 mbar
was average, as that's what barometers always used to have as the
central reading ("change"), but Wikipedia says it's 1013. I've seen some
newer ones with 1010 as the centre.

A bar is not defined as 1 atmosphere (average) pressure. Just happens to
be close (within 1% of it).
1 bar is equivalent to 100 kPa where 1 Pa (Pascal) is a defined SI unit
pressure of 1 Newton per m2.